Mixer for gas burners



Oct; 20, 1953 L. G. M. LE RENARD 2,655,992

MIXER FOR GAS BURNERS Filed Nov. 6, 1947 INVENTOR. L0 015 G-M-LQRENBRD (DECEASED) a 1O 3 Z Z a V y Armlw Patented Oct. 20, 1953 NUXER FOR GAS BURNERS Louis Georges Mathieu Le Renard, deceased, late of Paris, France, by Suzanne Simone Denise Le Renard ne Herrenschmidt, administratrix," Paris, France, assignor to LAir Liquide, 80- ciete Anonyme pour IEtude -et lEx-p'loitationdes Procedes Georges Claude, Paris, France,- a joint-stock company of France Application November 6, 1947, Serial No. 784,486

In France November '6, 1946 8 Claims.

The present invention relates to improvements in gas burners in which the gases are pre-mixed, in particular to welding or cutting 'blowpipes, with a view to avoiding what are called flashbacks or injector ignition. Devices are known, located either in the induced gas or in the mixture of both gases, for overcoming these drawbacks without causing an excessive loss of pressure head. These devices give good results for blowpipeswhich operate under a feed pressure for the drawn-in gas coming within the range of pressures 'for which they have been designed; for example, so called low-pressure oxy-acetylene blowpipesare designed for feed pressures of 8 grams per square centimetre and with the aforementioned devices, they operate without flash backs at all pressures between and 100 grams per square centimetre; However, it has been found that th'isis no longer true when the upper limit "of the normal operating pressure ofa blowpipeis substantially exceeded, for example when, in the case of the above blowpipes, use is made as the induced gas, of acetylene reaching the blowpipe under high pressure, for example, 400 grams per square centimetre.

The object of the present 'inventionis to overcome this drawback and, therefore,- to'increase the scope of useof the burners inques- 'tion;

For gas burners in which the gases are premixed, and which are already provided-with the aforesaid devices with a view to avoiding flashbacks, the invention consists in providing for the gas which acts as "an impeller, or inducing gas, inlet ducts having a section, a length and. ,l

a shape which will ensure laminary'flow of said inducing gas through said ducts.- These ducts are arranged either in the blowpipe handle or in the inducing gas inlet piping to the blowpipe burner in case it is not-provided'w-ith a handle,

and in all cases, in that portion of the handle or of the piping which immediately precedes the injector.

If, for structural reasons, it is not 'possible'to place thein'jector and the ducts according to the invention in the immediatevic'inity of one another, these ducts are placed at a certain distance, preferably as short as possible, upstream with respect to the injector and 'it'is then necessary that flow shall remain laminary between the downstream .endof these ducts and the injector, that 'is,..said .flow shall .not assume an unstable formwhich is intermediary between laminary flow and turbulent flow.

In the gas burners of the type referred to 2 above, the ducts have, for manufacturing reasons, diameters whichare large relative to their length and, hence, the ducts do not permit la-minary flow of gases therethrough. As already stated, when the pressure of the induc'ed gas (acetylene for instance? 'is-high,-flas'hbacks occur. By providing for the inducing gas (oxygen for instance) a lammary-"flow, said gas passes through the injector with an increased speed and enters the mixer at a great speedlso that the speed of the mixture of the induced and inducing gases is always greater than the speed of propagation of the flame through. said mixture. Consequently, flashbacks do not "occur. According to the invention, one or several members are placed within the duct for the burner inducing gas of present-day blowpipes (which duct, owing to its usual circular shape anddiameter, does not per se ensure a laminary flow for the gas), whichmembers form with the said duct a plurality of ducts which enable laminary flow to be obtained; these members may, for example, be located in the duct passing through the blowpipe handle. It has been found that the length of each-such duct should 'be at least equal to ten times its greatest transverse dimension.

With aviewto avoiding an excessive losssof pressure head in these-ducts, theemember's in question are of reducedthickness, say. onemillimetre. I

It should be pointed out that, in most. Lexyacetylene blowpipes, thenfiow of-acety1ene is laminary as a result ofitslpassage through the annular channel between (the injector and the mixer, and-also due to the section,.,the .shape and the length of said channel; howeven it has been found thatthis arrangement, although necessary, is not sufficient to avoid flash' backs, even when making use of the aforesaid devices; the arrangement according to the inventidncdntributes, in such case, in providing adequate safety when added to these devices.

The figures of the. accompanying, drawing show various forms of embodiment .of .the inventionin the .caseof an oxy-acetylene .blowpipevin which the oxygen serves as the inducing gasp.

Figure .1 .is a longitudinal-section :of ,the irear section of the blowpipe'from :the mixer tothe inlets for the two gases intofithezblowpiper Figure 2 is a section taken along thea plane AA'of Figure 1. r

Figures 3 and '4 show; in section, alongtl ris same planeA-A, other forms-of embodiment of the present invention:

According to Figurelitheoxygen' acting'asan inducing gas is introduced under pressure into the blowpipe handle i, through the connection 2 and enters the rectilinear duct 3 which passes through the handle. This duct does not per se ensure a laminary fiow of the oxygen. To accomplish such laminary fiow, the duct is provided.

with an internal tube 4, the wall of which is one millimetre thick and which may be made of metal. The ends 5, 5' of said tube are split in the form of a cross and are bent back so as to bear on the wall of the duct 3 and thus prevent said tube from shifting in position. The length of said tube 4 is ten times its inner diameter or ten times the difference between the inner diameter of the duct 3 and the outer diameter of 4; whichever of these two values is the larger.

tube, A2 is the area of the cross-section between the outer wall of the tube and the inner wall of the duct, (11 is the inner diameter of the tube, (12

is the outer diameter of the tube, and d: is the inner diameter of the duct, but

then

4 {media V 71111 .7F(d3+d2) cancelling, we have d d mai or the inner diameter of the tube is equal to the diflerence between the inner diameter of the duct and the outer diameter of the tube. In other words, the hydraulic radii of the tube passage within the tube and the annular passage between the tube and the duct wall are equal.

The oxygen issuing from the conduits 3 and 4 in the form of laminary streams fiows into the injector 1 through the conduit 6; this conduit 6, which is of small section, does not transform this laminar flow into an unstable flow preceding turbulent flow, or into a turbulent flow because its length is under ten times its diameter,

and it has been found that when a laminary i flow of the oxygen into the injector as far as the immediate proximity of the orifice 1' thereof.

Theacetylene flows through the conduit 8 passing through the blowpipe handle under a pressure of about 400 grams per cm and it is drawn in by the oxygen flowing out of the injector orifice T,

which is adjustable, for example by means of a needle valve 9, and the oxy-acetylene mixture flows throughthe mixer i0. During its travel around the annular-shaped injector, the. acetylenehasalaminaryfiow.f

According to Figure 3, the member 4a in troduced into the duct 3a is a thin strip having a section in the shape of a Z, the ends, of which are more or less held against movement in the duct by friction. 7

According to Figure 4, this member 4?) has a cross-section in the shape of two Zs crossing each other and it is made of two trough parts united by means of a few, tack welds.

In both the latter examples, the length of these members is equal to ten times the largest transverse dimension of each duct thus obtained, that is, ten times the diameter of the duct 3a in respect of Fig. 3, and ten times the radius of the duct 3b in respect of Fig. 4.

I claim: c

l. A gas burner having an injector, a mixer, means including a first duct for carrying a combustible gas to the injector, means including a second duct for carrying a combustion-supporting gas to the injector, said means including said first duct, said means including said second duct, and said injector being so constructed and arranged that the combustion-supporting gas acts as the inducing gas and the combustible gas acts as the induced gas in the injector, and a laminar flow-producing structure in said second duct comprising at least one elongated member extending rectilinearly longitudinally thereof and substantially coextensive therewith, said elongated member being of such configuration that said second duct is divided into a plurality of parallel passages, the lengths of said passages being at least ten times as great as their largest transverse dimensions, whereby the combustion-supporting gas passing therethrough to the injector is maintained in a laminar state. I

2. The apparatus defined in claim 1 in which said elongated member is a cylindrical tube spaced from the duct wall to provide a central passage within the tube and an annular passage between the tube and the duct wall.

3. The apparatus of claim-2 in which each end of said tube has longitudinally-seperated sections splayed outwardly to bearagainst the inner wall of said second duct. 7

4. The apparatus of claim 1 in which said elongated member is a cylindrical tube spaced from the wall of said second duct to provide a central passage within the tube and an annular passage between the tube and the duct wall, said second duct and said tube being of such dimensions that the hydraulic radii of said central passage and said annular passage are equal.

5. The apparatus of claim 1 in which said elongated member has a substantially Z-shaped cross-section.

6. The apparatus of claim 1 in which said elongated member has a cross-section substantially in the form of two inter-connected Zs.

' 7. A gas burner having an injector, a mixer, a first duct extending substantially parallel to the injector for supplying a combustible gas thereto,

. a second duct extending substantially parallel to theinjector and said first duct for supplying .a combustion-supporting gas to the injector, and a pair of spaced transversely-extending conduits connecting said first and second ducts, respectively, to said injector, the transversely extending conduit connecting the second duct to the injector having a length lessthan ten times its transverse dimension, and a laminar flow-producing structure in said second gas .duct comprising at least one elongated member extending rectilinear- 1y ,longitudmally thereof and substantially coexa tensive therewith, said elongated member being of such configuration that said second duct is divided into a plurality of parallel passages, the length of each of said passages being at least ten times as great as the largest transverse dimension of the passage, so that the combustion-supporting gas passing through said passage is maintained in a laminar state.

8. A gas burner including an injector having a central passage and an annular passage surrounding the central passage, a mixer to which said central passage and said annular passage lead, a first duct connected at one end to the annular passage in the injector for supplying a combustible gas to the mixer, a second duct con- 10 nected at one end to the central passage in the injector for supplying a combustion-supporting gas to the mixer, and a laminar flow-producing structure in said second gas duct comprising at least one elongated member within said second duct extending rectilinearly longitudinally thereof and substantially coextensive therewith, said elongated member being of such configuration that said second duct is divided into a plurality of parallel passages, the length of each of said passages being at least ten times as great as the largest transverse dimension of the passage, so that the combustion-supporting as passing through said passages is maintained in a laminar state.

SUZANNE SIMONE DENISE LE RENARD NEE HERRENSCHMIDT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 804,002 Fouche Nov. 7. 1905 887,467 Delcampe May 12, 1908 931,623 Kimball Aug. 17, 1909 1,029,691 Kirkwood June 18, 1912 1,194,740 Hunter Aug. 15, 1916 1,361,804 Adams Dec. 14, 1920 1,400,024 Caracristi Dec. 13, 1921 1,645,337 Messer Oct. 11, 1927 1,994,841 Thomas Mar. 19, 1935 2,389,166 'Seaver Nov. 20, 1945 FOREIGN PATENTS Number Country Date 8,320 Great Britain of 1894 

